Lecture 4 Physiology of the Heart III Flashcards Preview

CDL301 Cardiovascular Pharmacology > Lecture 4 Physiology of the Heart III > Flashcards

Flashcards in Lecture 4 Physiology of the Heart III Deck (45)
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1

The main coronary arteries are the first branches of the aorta T or F

T

2

Describe how coronary arteries project over and perfuse the heart

The coronary arteries run over the surface of the heart and then perforate into the muscle itself

3

What is unusual about the perfusion by the coronary arteries

The coronary blood flow occurs during diastole. In systole the vessels are squashed by the contracting cardiac muscle

4

Anything increasing left ventricular end diastolic pressure will have what effect on coronary artery perfusion

Anything increasing LVEDP will diminish perfusion of the coronary arteries

5

What can be said about the relationship between cardiac output and coronary oxygen consumption

Oxygen consumption increases in parallel to cardiac output. Cardiac output can increase 7-fold during exercise and similarly oxygen consumption increases 7/8-fold during exercise

6

Recall the equation for cardiac oxygen delivery

Oxygen delivery = arterial oxygen concentration x coronary blood flow

7

Using the equation and in theory what two aspects can be changed in order to increase oxygen delivery to the coronary arteries

Can increase the arterial oxygen concentration or increase the coronary blood flow or both

8

Why is it that the primary determinant of oxygen delivery to the heart is coronary blood flow and not arterial oxygen concentration

There is relatively little oxygen dissolved in blood plasma and so arterial oxygen concentration is mainly determined by the oxygen bound to haemoglobin. Ordinarily there is little change in the oxygen content of arterial blood with oxygen saturation remaining high at around 98%

9

What is the standard arterial systolic pressure

120mmHg

10

What is the standard arterial diastolic pressure

80mmHg

11

Why is the standard arterial diastolic pressure not 0mmHg

Diastolic pressure is not 0mmHg in the arteries because of the closed aortic valve. Without the aortic valve the diastolic pressure would drop to zero and you wouldn’t be able to perfuse the coronary arteries.

12

What is the dicrotic notch

The dicrotic notch is a secondary upstroke in the descending part of an arterial blood pressure trace. This corresponds to the transient increase in aortic pressure upon closure of the aortic valve

13

Pressures in the aorta indicative of all the arteries of the body T or F

T

14

How does the systolic pressure of the ventricles compare to the arterial systolic pressure

The systolic pressure in the ventricles should be exactly the same as the aorta around 120mmHg. This is because at this point the aortic valve offers no resistance to flow and hence anything generated in the ventricle will be reflected in the aorta

15

How does the diastolic pressure of the ventricles compare to the arterial diastolic pressure

It’s a lot less. As the ventricles contract they expel the blood so that upon relaxation in diastole there is nothing to support much pressure

16

What is the approximate value of ventricular diastolic pressure

Roughly 5-8mmHg

17

What feature of the arterial and ventricular pressures causes the perfusion of the coronary arteries

The difference in arterial diastolic pressure and left ventricular end diastolic pressure is what causes the perfusion of the coronary arteries

18

Which ventricular pressure is considered when talking about the perfusion of the coronary arteries

The left ventricular pressure

19

What three factors can change coronary flow

Physical factors (pressure gradients) local metabolites and nervous/humoral factors

20

Draw a diagram depicting the arterial and left ventricular pressures in diastole and systole highlighting the region where coronary flow occurs

See completed diagram below – coronary flow window indicated in yellow

21

What changes increase the window of coronary blood flow perfusion

Increases in the time between systole and diastole and increases in the difference in diastolic pressure between the aorta and ventricles

22

What are the effects of tachycardia on coronary perfusion

Tachycardia disproportionately reduces the time of diastole which in turn decreases coronary perfusion

23

What are the effects of a raised LVEDP on coronary perfusion

Raised left ventricular end diastolic pressure decreases the difference in diastolic pressure which in turn decreases coronary perfusion

24

What are the effects of reduced arterial diastolic pressure on coronary perfusion

Decreased arterial diastolic pressure decreases the difference in diastolic pressure which in turn decreases coronary perfusion

25

What is meant by autoregulation

Autoregulation is the ability of an organ to maintain a constant blood flow despite changes in perfusion pressure

26

Describe the changes in blood flow and resistance that is seen as a result of autoregulation in response to a fall in perfusion pressure in the heart

Because flow is proportional to perfusion pressure a drop in perfusion pressure will result in the blood flow also dropping. Interestingly because the blood vessels are capacitive there is an initial small increase in resistance. However autoregulation in the heart means that resistance then decreases. This acts to restores the flow back up due to the inverse relationship between resistance and flow. This flow is then maintained despite the reduced pressure

27

What events can case a drop in perfusion pressure

Heart attack septic shock haemorrhaging

28

How is the drop in resistance in the heart in response to a drop in blood flow detected and mediated by the heart during autoregulation

In response to a decrease in flow the heart detects the decrease in pO2 reaching it and then triggers the generation of metabolites to causes vasodilatation. Vasodilation in turn decreases the resistance of the vessel

29

Which is the most important mechanism of day-to-day control of coronary flow

Vascular control through the release of metabolites and mediators

30

What evidence lead to the indication that local mediators must be responsible for the vascular control of coronary perfusion

In response to hypoxia there is a marked coronary vasodilatation in situ but not in isolated coronary arteries in vitro. This implies that the vasodilation is not a property of the coronary arteries themselves